Not applicable.
1. Field of the Invention
The present invention relates generally to disk drives, and in particular to a disk drive including spindle motor hub having an equivalent MR read element bias voltage to mitigate a voltage potential between a disk and the MR read element.
2. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes the disk drive base, a cover, at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA).
The spindle motor includes a spindle motor hub that is rotatably attached to the disk drive base. The spindle motor hub has an outer hub flange that supports a lowermost one of the disks. Additional disks may be stacked and separated with annular disk spacers that are disposed about the spindle motor hub. The spindle motor typically includes a spindle motor base that is attached to the disk drive base. A shaft is coupled to the spindle motor base and the spindle motor hub surrounds the shaft. The spindle motor hub may be rotatably coupled to the shaft and therefore the spindle motor base typically via a pair of bearing sets. A stator is positioned about the shaft and is attached to the spindle motor base. A magnet element is attached to the hub flange. The stator includes windings that selectively conduct current to create a magnetic field that interacts with the various poles of the magnet element. Such interaction results in forces applied to the spindle motor hub that tend to rotate the spindle motor hub and the attached disks.
The head stack assembly has an actuator assembly having at least one head or slider, typically several, for reading and writing data to and from the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached sliders are moved relative to tracks disposed upon the disk.
The head stack assembly includes the actuator assembly and a flex circuit cable assembly that are attached to the actuator assembly. A conventional xe2x80x9crotaryxe2x80x9d or xe2x80x9cswing-typexe2x80x9d actuator assembly typically comprises an actuator body, a pivot bearing cartridge, a coil portion that extends from one side of the actuator body to interact with one or more permanent magnets to form a voice coil motor, and one or more actuator arms which that extend from an opposite side of the actuator body. The actuator body includes a bore and the pivot bearing cartridge engaged within the bore for allowing the actuator body to rotate between limited positions. At least one head gimbal assembly (xe2x80x9cHGAxe2x80x9d) is distally attached to each of the actuator arms.
A head gimbal assembly includes the slider that is attached to a suspension with a gimbal. Typically the slider is of an air bearing slider design. In a contemporary design for the slider, the slider includes embedded within it a magneto-resistive (xe2x80x9cMRxe2x80x9d) read element and an inductive write element. The term MR read element additionally refers to giant magneto-resistive (xe2x80x9cGMRxe2x80x9d), enormous magneto-resistive (xe2x80x9cEMRxe2x80x9d), and similar functioning devices. The HGA is configured such-that the slider, and therefore the MR read element, xe2x80x9cfliesxe2x80x9d above a given track of a given magnetic disk.
The MR read element effectively may take the form of a resistor having a hard magnetic bias associated with it. The resistor changes in resistance to electrical current as a function of magnetic flux intercepted by it. In this regard, the tracks disposed upon each magnetic disk represent magnetically polarized regions. The resistance of the resistor is increased when it is disposed immediately adjacent magnetically polarized regions. As portions of the magnetic disk rotate past the MR read element, the polarity of the magnetic field in which the MR read element is exposed changes. In response, the MR read element tends to repel or attract in relation to the magnetic disk due to the hard magnetic bias. This places an internal stress on the MR read element that changes its resistance. During a reading operation, current is applied through the MR read element. The resulting changes in the resistance of the MR read element affect the current flowing through it. Thus, information on the magnetic disk is decoded by monitoring the current that flows through the MR read element.
It is desirable to apply a bias voltage (a voltage other than zero) to the MR read element. This increases the signal to noise ratio for mitigating the effect of ground noise, and tends to stabilize the associated electronic circuit. However, the magnetic disk is connected to electrical ground and this results in a voltage potential between the MR read element and the magnetic disk. Due to the close proximity of the slider, and therefore the embedded MR read element, to the magnetic disk (e.g., 0.4 micro-inches), the slider is susceptible to certain electronic overstress (xe2x80x9cEOSxe2x80x9d) events. For example, the dielectric strength of air may be overcome resulting in an electrical arc from the MR read element to the magnetic disk or the slider may come into contact with the magnetic disk. This results in a current from the MR read element to the magnetic disk that has an electro de-plating effect upon the MR read element, thereby changing the electrical properties of the MR read element. Proper performance of the MR read element is predicated upon the MR read element having specified electrical properties. As such EOS events change the electrical properties of the MR read element, this has a negative impact upon the performance of the MR read element. Accordingly, there is a need in the art for an improved MR read element arrangement in comparison to the prior art.
An aspect of the invention can be regarded as a disk drive that includes a disk drive base and a magnetic disk. The disk drive further includes a rotary actuator coupled to the disk drive base. The rotary actuator has an MR read element disposed adjacent the magnetic disk. The MR to read element has a bias voltage. The disk drive further includes a rotatable spindle motor hub for rotating the magnetic disk positioned on the spindle motor hub. The spindle motor hub is in electrical communication with the magnetic disk. The spindle motor hub is mechanically coupled to and electrically insulated from the disk drive base. The disk drive further includes a circuit for applying a voltage equivalent to the bias voltage to the spindle motor hub such that a voltage potential between the MR read element and the magnetic disk is mitigated.
The disk drive may further include a shaft rotatably coupled to the spindle motor hub and a cover attached to the disk drive base, the cover being mechanically coupled to and electrically insulated from the shaft. A screw may be provided and the cover includes a screw hole. The screw is axially engaged with the shaft through the screw hole-and the screw is electrically insulated from the cover. According to an embodiment of the present invention an electrically insulative grommet may be provided which is engaged within the screw hole. The grommet is sized and configured to receive the screw for electrically insulating the cover from the screw. In an alternative embodiment, the screw may be formed of an electrically insulative material, such as a plastic or ceramic material. The disk drive may further include an electrically insulative spacer disposed between the cover and the shaft and sized and configured to receive the screw for preventing electrical contact between the cover and the shaft.
The disk drive may further include a spindle motor base. The spindle motor hub is rotatably coupled to the spindle motor base. The spindle motor base is mechanically coupled to and electrically insulated from the disk drive base. According to an embodiment of the present invention, the disk drive further includes an electrically insulative gasket disposed between the spindle motor base and disk drive base for electrically insulating the spindle motor base from the disk drive base. In an alternative embodiment, the spindle motor base is formed of an electrically no insulative material, such as an injection molded plastic material.
The disk drive may further include a pre-amplifier in electrical communication with the MR read element for applying a bias voltage to the MR read element. The circuit for applying a voltage equivalent to the bias voltage is in electrical communication with the pre-amplifier. The circuit for applying a voltage equivalent to the bias voltage may include an amplifier filter network for generating a voltage equivalent to the bias voltage.